Method and apparatus for connection of stimulus and recording electrodes of a multi-channel nerve integrity monitoring system

ABSTRACT

The invention provides a method and apparatus for connecting multiple electrodes into the receiving or head box portion of the nerve integrity monitor. The invention may provide patient connection electrodes, their transmission lines and a manner by which these components may communicate to the main monitoring unit to actuate automatic setup functions and instructions. The “off-line” setup and diagnostic instructions may be automatically initiated and annunciated to the main portion of the intraoperative nerve integrity monitor. The setup and diagnostic instructions may then automatically executed. The invention also may provide patient connection electrodes with improved resistance to the deleterious effects of spurious electromagnetic artifacts. The invention may also include the incorporation of both stimulation and recording electrodes with a single cable, but with the head boxes for recording and stimulation arranged in a staggered fashion along that cable. The recording electrode portion may appear at the terminal end of the cable and can be placed at the site of recording electrode placement. This arrangement allows use of shorter length electrodes, which may be cheaper to construct and less susceptible to electromagnetic and mechanical (drape movement) artifacts. The stimulus portion may be positioned more proximate to the main unit by several feet. After the recording portion is properly positioned, the stimulus connection box may be approximately at its optimal positioning for access after surgical draping. The all-in-one construction would obviate the need to separately place a stimulus head box apparatus, as for devices that include separate recording and stimulation head boxes and associated cabling. The invention may be particularly applicable for use in monitoring facial electromyograhic (EMG) activity during surgeries in which a facial motor nerve is at risk due to unintentional manipulation, as well as for other neural monitoring procedures.

This non-provisional application claims the benefit of U.S. ProvisionalApplication No. 60/069,877, filed Dec. 16, 1997, and is acontinuation-in-part of U.S. patent application Ser. No. 09/212,380, nowU.S. Pat. No. 6,181,961, the subject matter of each being incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to multi-channel nerve integrity monitoring, andmore particularly to the patient connection electrodes, theirtransmission lines and a manner by which these components may beconnected and communicate to the main monitoring unit to actuateautomatic setup functions.

2. Description of Related Art

Despite advances in diagnostic, microsurgical and neurologicaltechniques that enable a more positive anatomical identification offacial nerves, following surgical procedures to the head and neck, suchas an acoustic neuroma resection, there is a significant risk of apatient losing facial nerve function. Because of the very delicatenature of these facial nerves, even the best and most experiencedsurgeons using the most sophisticated equipment known, encounter aconsiderable hazard that one or several nerves will be bruised,stretched or severed, during an operation.

However, studies have shown that preservation of facial nerves during anacoustic neuroma resection, for example, may be enhanced by the use ofintraoperative electrical stimulation to assist in locating nerves.Broadly stated, the locating procedure, also known as nerve integritymonitoring, involves inserting sensing or recording electrodes directlywithin the cranial muscles innervated or controlled by the nerve ofinterest. Such an exemplary monitoring electrode is disclosed in U.S.Pat. No. 5,161,533 to Prass et al., which is incorporated herein byreference in its entirety.

One method of nerve localization involves the application of electricalstimulation near the area where the subject nerve is believed to belocated. If the stimulation probe contacts or is located in the areareasonably close to the nerve, the stimulation signal applied to thenerve is transmitted through the nerve to excite the related muscle.Excitement of the muscle causes an electrical impulse to be generatedwithin the muscle that is then transferred to the recording electrodes,thereby providing an indication to the surgeon as to the location of thenerve. Stimulation is accomplished using handheld monopolar or bipolarprobes, such as the Electrical Stimulus Probe described in U.S. Pat. No.4,892,105 to Prass, which is incorporated herein by reference in itsentirety.

The Electrical Stimulus Probe (now known as the “Prass Flush-TipMonopolar Probe”) is insulated up to the distal tip to minimize currentshunting through undesired paths. Another example of a bipolar probe isdescribed in the U.S. Provisional Patent Application No. 60/096,243,entitled “Bipolar Electrical Stimulus Probe”, filed Aug. 12, 1998, whichis incorporated herein by reference in its entirety.

Another method of nerve localization involves the mechanical stimulationof the nerve of interest by various dissecting instruments. Directphysical manipulation of a motor nerve may cause the nerve to conduct anerve impulse to its associated musculature. If those muscles are beingmonitored using a nerve integrity monitoring instrument, the surgeonwill hear an acoustic representation of the muscle response in closetemporal relationship to the antecedent mechanical stimulation. Thiswill allow the nerve of interest to be roughly localized at the contactsurface of the dissecting instrument.

Prior art nerve integrity monitoring instruments (such as the Xomed®NIM-2® XL Nerve Integrity Monitor) have proven to be effective forperforming the basic functions associated with nerve integritymonitoring, such as recording Electromyogram (EMG) activity from musclesinnervated by an affected nerve and alerting a surgeon when the affectednerve is activated by application of a stimulus signal. However, thesenerve integrity monitoring instruments have significant limitations forsome surgical applications and in some operating room environments, asdiscussed below.

For example, a significant limitation in the majority of prior art nerveintegrity monitoring devices is the availability of only two channelsfor monitoring of EMG activity. This two channels monitoring capabilityprovides a limited ability to monitor multiple nerves or multiplebranches of single nerves. In addition, a limited number of channelsdoes not allow for redundancy in the event of electrode failure.

In some cases, such as with monitoring the facial nerve during theperformance of parotidectomy, monitoring must be performed from each offour major branches of the facial nerve. Alternatively, proceduresinvolving the more proximal (closer to the brainstem origin) portion ofthe facial nerve may be effectively monitored by a single channel, inthat the nerve exhibits no topographical organization in that location.With only two channels available, there is also limited ability todistinguish whether recorded signal events represent artifacts or EMGresponses, based upon their distribution among “intelligent” and“non-intelligent” electrodes, as described in U.S. patent applicationSer. No. 09/213,015, filed on Dec. 16, 1998. That is, true or importantEMG signals provoked by surgical manipulations distribute“intelligently” only to muscles supplied by the nerve of interest. Incontrast, electrical artifacts distribute “non-intelligently” to allproximate electrodes within an electrical or electromagnetic field. Thusa multi-channel recording capability allows the user to distinguishartifacts and EMG signal events on the basis of such distribution.

Another advantage of multi-channel recording is that, with theavailability of some redundancy, different recording strategies may beused for recording signals from the muscles supplied by a single nerveof interest, in order to take advantage of their respective advantagesand minimize their inherent disadvantages. The most commonly usedrecording method for intraoperative nerve integrity monitoring involvesintramuscular placement of two closely spaced electrodes. The use ofintramuscular electrodes in close bipolar arrangement (as described inU.S. Pat. No. 5,161,533) is preferred in order to obtain adequatespatial selectivity and maintenance of high common mode rejectioncharacteristics in the signal conditioning pathway for reducedinterference by electromagnetic artifacts. Such electrode configurationsyield a compressed dynamic range of electrical voltage observed betweenthe paired electrodes. For example, if it is physically situated nearone of the electrodes, a single motor unit (activation of a single nervefiber) may cause an adequate voltage deflection to be heard as a clearsignal spike or to exceed a predetermined voltage threshold. Moreover,with close electrode spacing and bipolar amplification, recording oflarger responses is frequently associated with internal signalcancellation, which significantly reduces the amplitude of the observedelectrical signal. The resultant compressed dynamic range isadvantageous for supplying direct or raw EMG signal feedback to theoperating surgeon, in that both large and small signal events may beclearly and comfortably heard at one volume setting. However, the methodoffers a limited ability to fractionate responses based upon theiroverall magnitude.

For quantitative measurements of EMG response amplitudes, a preferentialrecording method involves the use of surface electrodes in a monopolararrangement, with an active electrode placed over a suitable muscle,supplied by the nerve of interest, and the other electrode placed at arelative distance away in an electrically neutral site. The activeelectrode summates muscle activity over a greater or more representativearea than intramuscular electrodes and the absence of a simultaneoussignal in the inactive (“indifferent reference”) electrode eliminatesunpredictable signal cancellation seen in bipolar recording where bothelectrodes in a pair detect the same signal from different perspectives.Measurement of the response amplitude using this recording methodprovides an excellent representative measure of relative magnitude ofmuscle activation. However, the monopolar (“indifferent reference”)arrangement with surface electrodes provides a poor quality signal foracoustic (loudspeaker) feedback to the operating surgeon. Withmulti-channel recording capability, this method of EMG recording may beemployed in parallel with closely spaced intramuscular electrodes inorder to achieve better signal quality

With the stated potential advantages afforded by multi-channel recordingcapability, some devices are known to include up to eight channels ofEMG recording capability. However, while multi-channel recording affordsthe possible advantages stated above, it poses a significantdisadvantage of requiring greater complexity of off-line diagnostic orsystem check, and recording setup procedures. This is especially true ifcertain channels are designated for quantitative purposes using amonopolar method and others are used for feedback to the operatingsurgeon with closely spaced intramuscular electrodes. Thus, a method isneeded that would allow a surgeon to take advantage of the flexibilityafforded by a multi-channel EMG recording capability, while reducing therelative complexty of setup and diagnostic functions.

Another problem posed by the availability of a greater number of EMGrecording channels, in the setting of coventional art, is that allelectrodes are provided individually or in kits with separate connectorsfor each lead. Furthermore, “protected” pin connectors required byconventional devices are more bulky and cumbersome to use than the“standard” pin connectors. Regardless of color coding and other labelingstrategies, with multiple recording electrodes, placing the connectorpins in the electrode receiving portion (“head box”) of the nerveintegrity monitor can be quite tedious, time consuming, and confusing,such this configuration may result inaccuracy regarding proper placementof the connectors.

Another problem related to multiple channel recording is that the headbox portion of the nerve integrity monitoring, which receives theelectrodes placed in various locations on the patient, must be of asufficient size to accommodate all of the necessary connections. Thelarger size of the head box may render it more susceptible toelectromagnetic noise and may be too large to allow it to be placedphysically near the area where the electrodes are placed. Multiplechannel head boxes are typically placed under the operating table,because they cannot be placed close to the electrode sites.

Accordingly, the remote location of the head box results in electrodeleads being typically one meter in length or longer. Electrode leads aretypically unshielded from the effects of electromagnetic noise, and thelonger the length of the leads, the more susceptible they are to suchinterference. One method of improving the resistance of electrode leadsto electromagnetic noise is to arrange them in a “twisted-pair” fashion,as described in U.S. Pat. No. 5,161,533. Such an arrangement betterpreserves common mode rejection capabilities within the signal path thanotherwise untreated leads. Therefore, a method that allows reduction ofthe size of the head box apparatus or otherwise further reduces thepotential electromagnetic interference in the electrode leads would bedesired.

SUMMARY OF THE INVENTION

The invention provides a method and apparatus for connecting multipleelectrodes into the receiving or head box portion of the nerve integritymonitor. The invention may provide patient connection electrodes, theirtransmission lines and a manner by which these components maycommunicate to the main monitoring unit to actuate automatic setupfunctions and instructions. The “off-line” setup and diagnosticinstructions may be automatically initiated and annunciated to the mainportion of the intraoperative nerve integrity monitor. The setup anddiagnostic instructions may then automatically executed. The inventionalso may provide patient connection electrodes with improved resistanceto the deleterious effects of spurious electromagnetic artifacts.

The invention may also include the incorporation of both stimulation andrecording electrodes with a single cable, but with the head boxes forrecording and stimulation arranged in a staggered fashion along thatcable. The recording electrode portion may appear at the terminal end ofthe cable and can be placed at the site of recording electrodeplacement. This arrangement allows use of shorter length electrodes,which may be cheaper to construct and less susceptible toelectromagnetic and mechanical (drape movement) artifacts. The stimulusportion may be positioned more proximate to the main unit by severalfeet. After the recording portion is properly positioned, the stimulusconnection box may be approximately at its optimal positioning foraccess after surgical draping. The all-in-one construction would obviatethe need to separately place a stimulus head box apparatus, as fordevices that include separate recording and stimulation head boxes andassociated cabling.

The invention is particularly applicable for use in monitoring facialelectromyograhic (EMG) activity during surgeries in which a facial motornerve is at risk due to unintentional manipulation, although it will beappreciated that the invention has broader applications and can be usedin other neural monitoring procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detailed with reference to the followingdrawings, wherein like numerals represent like elements, and wherein:

FIG. 1 is a diagram of an exemplary multi-electrode patient connectionapparatus;

FIG. 2 is a diagram of another exemplary multi-electrode patientconnection apparatus;;

FIGS. 3A-3G are diagrams of an exemplary patient connection recordingharness;

FIG. 4 is an exemplary block diagram of the automatic setup system;

FIG. 5 is an exemplary diagram of a connection system for stimulatingand recording electrodes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention embodies a method and apparatus by which the patientconnection procedure and other aspects of “off-line” setup prior tomulti-channel nerve integrity monitoring is made simpler, lesscumbersome, and less time-consuming. The patient connection procedureand “off-line” setup is based upon the construction of specialmulti-electrode patient-connection (“kits”), a patient connectionharness and the manner by which certain aspects of thepatient-connection kits communicate specific information to the mainportion of the nerve integrity monitor regarding setup parameters. Theconstruction of the patient connection kits and harness also reduces thelikelihood of electromagnetic interference than with standard electrodeconnections. In the discussion below, there is a relatively strongconceptual separation between off-line control (performed at some timeother than during the surgical procedure) and on-line control (performedduring a surgical procedure), as pertains to control of intraoperativeneurophysiological monitoring system functions through the use of inputdevices. For purposes of the discussion below, “off-line” operations areperformed when monitoring is not actively being performed, for example,as when logging-in patient information, setting system preferences orretrieving saved-data for “post-production” analysis, whereas “on-line”refers to periods of active intraoperative neurophysiologicalmonitoring, which involves the monitoring functions of nervelocalization and function assessment. The use of the present inventionpertains to, but is not limited to, “off-line” control of functions ofthe intraoperative nerve integrity monitor.

FIG. 1 is an exemplary diagram of a multi-electrode patient-connectionapparatus (or “kit”) 100 with four paired bipolar “intelligent” dataelectrodes and one artifact-detection electrode (“4+1”). All electrodesterminate in conductor strips or electrical contacts 101 on a connector105 constructed (a male connector is shown as an exemplary connector inthis embodiment) from double-sided PC board stock, for example. Theconnector 105 contains a notch 110 or other irregular feature that maybe used to firmly hold the connector in the proper position by aspring-loaded latch. One pair of contacts 101 on the connector 105 isshorted by a jumper 115, or any other electrical connection providing anequivalent function. One unpaired connection is made with a singlepatient ground electrode 120. In the present embodiment, there are fourpaired bipolar electrodes 125 and one artifact-detection electrode 130.When the connector 105 is connected to the main monitoring unit,electrical contact with the circuitry in the main monitoring unit by theelectrical contacts 101, signals the initiation of the automatic setup.

As described above, for the purposes of the description of FIG. 1 aboveand FIG. 2 below, multiple recording electrodes 125,130, soldered orotherwise pre-connected to a multi-pin (contact) connector, will betermed a kit 100. Each kit 100 consists of the above-described multipleEMG recording electrodes 125, a single artifact-detection electrode 130,a single patient ground electrode 120 and a single multi-contactconnector with compact dimensions.

The length of the EMG electrode leads 125 is 18 inches, which isapproximately one-half of the length of conventional electrodes. Thus,the EMG electrodes 125 of the invention are less susceptible toelectromagnetic noise. The single 1 cm (subdermal) ground electrode 120is also 18 inches in length or somewhat greater. The artifact-detectionelectrode 130 is 24 inches greater in length in order that the leads maybe looped over the area where the other EMG electrodes 125 are inserted,thus, creating a mild antenna effect for detecting electromagneticartifacts.

Within the connector 105 of the patient-connection kits 100 are multipleadditional pairs of contacts 101, across which there may be no (or anopen) connection. A short or jumper wire 115, or a fixed resistor ofvarying absolute value may be connected across the additional contactpairs 101 so that they may be shorted. In conjunction with the apparatusdescribed below, closure of these shorted contacts 101 serves as aconsistent signal to the main unit to initiate setup functions.

Alternatively, the connectors 105 of the patient-connection kit 100 maycontain limited circuitry with a small amount of non-volatile memory inaddition to the patient electrodes 125,130. The male portion of theconnector 105 is offset eccentrically so that there is obviously onlyone way to connect it with another device. The connector 105 alsocontains a notch (or other irregular feature) that allows it to latchwith its connection counterpart.

FIG. 2 is a exemplary diagram of another embodiment of a multi-electrodepatient-connection apparatus or kit 200 with only two paired bipolar“intelligent” data electrodes 230 and one artifact-detection electrode235 (“2+1”). As in FIG. 1, all electrodes 230,235 terminate in conductorstrips or contacts 201 on a connector 205. Two other conductor pairs areso connected by a jumper 220 that signals to the main nerve integritymonitoring unit that those channels are not to be used for EMGrecording. One unpaired connection is made with a single patient groundelectrode 225.

In FIGS. 3A-3G, the patient connection recording harness 300 connects tothe main chassis of the main monitoring unit by a male multi-pinconnector 301. A transmission line cable 305 contains multiple pairs ofwires, maximally treated for resisting electromagnetic artifact, apatient ground wire and multiple additional wire pairs. There is are-enforced flexible plastic protective covering 310 in order to providestrain relief as the cable enters the main housing of the receivingportion of the harness 325.

A button 320 on the side of the housing of the receiving unit 325releases connectors that are placed into the receiving unit. The housingof the receiving unit 325 accepts an adapter device 337, which permitsthe connection of individual patient electrodes that terminate instandard “protected” pin connectors. The adapter device 337 has a “male”connector portion 330, which is offset or constructed in such a mannerso as to limit the connection to only a single orientation. The maleconnector portion 330 may also have a slot or other feature 335 to allowa spring-loaded retainer to hold the electrode firmly within thereceiving housing 325.

On the terminal portion of the adapter device 337, the female connectorsfor accepting the “protected” pins of individual bipolar electrodes areclosely spaced and (for minimizing the overall size of the adapter)arranged in pairs 340. There is also an unpaired single terminus for apatient ground electrode 345. As illustrated in this exemplaryembodiment, the male portion 330 of the adapter 337 is made ofdouble-sided PC board stock. The conductor strips or contacts 350 matewith contacts on the inside of the receiving housing. Looking onto theface of the receiving housing shows a slot 355 to accept the maleconnector portion 330 of the adapter 337.

FIG. 4 illustrates an exemplary cable transmission line portion 400 ofthe harness apparatus 401 that carries multiple data channels, maximallytreated for resistance to electromagnetic field interference, a singlepatient ground electrode and at least three additional pairs ofelectrodes for communicating with the automatic setup apparatus. The“Harness” terminates in a male multi-connector 405 that mates with afemale counterpart in the main chassis housing of the nerve integritymonitor 410. All wires are routed through an impedance detection device415 that operates only during setup functions. EMG data is routed torecording amplifiers and DSP circuits 420. The electrode impedancemeasuring circuit 415 outputs to a controller/interface 425, whichstores a programmable series of setup instructions, held in“non-volatile” memory. Based upon the pattern of impedances measured,the controller/interface 425 communicates setup instructions andparameters to a digital stimulator 430, a system controller 435 and therecording section 420 of the nerve integrity monitor. The systemcontroller 435 can secondarily modify parameters, based upon other frontpanel (or other) input. Front panel indicators and audio displayfeatures 440 demonstrate results of diagnostics and important aspects ofsetup parameters.

The patient-connection harness pertains to a device that accepts theconnector of the kits and contains a long transmission line (wires) andeventually terminates in a multi-pin connection at the main nerveintegrity monitoring unit. The receiving portion of the harness is assmall as possible, preferably less than two or three inches in anydimension, in order that it may easily fit on top of the operating tablenext to the patient.

The receiving portion of the harness has an eccentric offset thatre-enforces a single orientation with the connector of thepatient-connection kits. There is also a latch mechanism that fits intoa notch located on the kit connector. A push-button mechanism allowsrelease of the latch upon depression. Otherwise, the kit connector isheld firmly within the receiving portion of the harness. Thetransmission line portion of the harness is 16 feet in length, forexample. This is to allow the main monitoring unit to be situatedapproximately 10 feet from the operating table. The remaining 6 feetallow the receiving portion of the harness to extend from the floor tothe top of the operating table. Within the transmission line of theharness the wires related to electrode data are maximally treated togive high resistance to electromagnetic interference. This is preferablyaccomplished with shielded, twisted pair wiring. However, othertreatments, such as individually shielded coaxial wires, are availableand effective. The wires related to the additional pairs of contacts onthe connector of the “kits” are treated with simple insulation andwithout individual shielding. The harness finally terminates in a malemulti-pin connector that mates with a female connector at the mainchassis of the nerve integrity monitor.

Inside the main chassis of the nerve integrity monitor, all electrodelead and additional lead pairs will be routed to an impedance detectioncircuit. Except for brief periods of activation, the impedance detectioncircuit allows a clean (low-noise) “pass-through” condition of the EMGelectrode signals. When the patient-connection kit is connected to theharness, the impedance detection circuit measures zero impedance for thecontact pair that is always shorted in the patient connection kits. Thissignal initiates automatic setup functions.

As part of the automatic setup function, the impedance detection circuitmeasures the impedance of each EMG electrode pair and for the additionalcontact pairs. Impedance information regarding EMG electrodes isdisplayed by front panel CRT or LCD screen. The results of impedancemeasurement for both the EMG electrode leads and the additional contactpairs is communicated to a software controller interface, which actuatesautomatic setup of stimulus, recording and quantitative assessmentparameters through a system controller, by triggering one of multiplestored setup algorithms. Preferably, these algorithms are stored onnon-volatile memory in order that the setup parameters will be resistantto line surges and accidental unplugging. The system controller mayindicate “pass” or “fail” of various internal diagnostic checks by frontpanel lighted indicators, audio tones, sound samples or voice samples.

The present embodiment is adapted to a monitoring device with four EMGdata channels and an artifact-detection electrode. By the describedmethod, the status of each of the additional contact pairs on theconnector of the patient-connection kits, among open, closed (shorted)or specific fixed resistance conditions, may be configured to inform themain unit of a particular intent on the part of the surgeon. Forexample, it might indicate that the surgeon has chosen a patientconnection kit, which is used for monitoring parotidectomy procedures,which involve a four channel setup and all four channels are displayedto the surgeon via loudspeaker.

Alternatively, in another embodiment of the kit, one of the pairedbipolar electrodes might be sacrificed in favor of a pair of surfaceelectrodes to be used monopolar (summating) arrangement for quantitativemeasurements. The status of impedance among the additional contact pairsmight inform the main unit that the channel involving surface electrodesshould not be included in audio feedback to the surgeon and that allquantitative determinations are to be routed to the “quantitative”channel. Still another embodiment might involve a kit containing two EMGelectrodes. The connector is the same as for four channel versions. Thelocations on the connector where two electrodes are omitted are shortedby a jumper, which provides additional signals to the main unitregarding a two-channel setup.

A preferred approach for automatic setup is for an initial “signature”sequence followed by a “diagnostic” sequence. The “signature” sequencerefers to a routine that involves lighting of channel and thresholdindication LED's and corresponding audio representations (if differenttones are sound designations are used for different channels) in anordered and recognizable sequence. During this sequence all channelindicators light (or blink) and audio indicators sound in sequence,regardless of any problems or how many electrodes are being used. Thisgives the user a “memory” or impression of full unit function.

During a second time through, termed here as a “diagnostic” sequence,the process is repeated. However, the unit stops in the sequence, whenit perceives a problem, such as with impedance mismatches or electrodedisconnection. The second sequence represents a diagnostic “review” ofimportant parameters. If a problem is perceived in one of the datachannels, the sequence stops and an indicator light might blink inrelation to the problem channel and an error message might appear in aCRT/LED display. Consistent sequences that route through the functionsof the unit will likely make the user more aware of proper and improperfunctioning of the unit.

The exemplary stimulating and recording electrode connection embodimentshown in FIG. 5 will now be discussed. Intraoperative nerve integritymonitoring involves the recording of electromyographic signals frommuscles supplied by nerves to be monitored during surgical procedures.In addition, a stimulus probe is used to apply small electrical currentsin order to locate and map the contour of the nerve to be monitored, aswell as, to assess nerve function. Nerve integrity monitoring devicesinclude both recording and stimulating functions.

In order to accomplish connection of the patient electrodes to its mainportion, monitoring devices provide either a single cable with a single(common) “head box” for attachment of both stimulus and recordingelectrodes. Alternatively, two separate cables and separate head boxesto separately accommodate recording and stimulus electrodes. The mostcommonly used devices employ the single head box configuration.

Recording electrodes are typically placed and connected to themonitoring device after general anesthesia, but before sterile drapingof the surgical field. Electrical stimulus probes are usually “passedoff” in a sterile fashion and connected to the monitoring device afterdraping has been completed. If both recording and stimulation are to beemployed, a head box with both recording and electrical stimulatingelectrode connections in a single housing must be placed where it can beaccessed after sterile surgical draping. This location is usuallysomewhere underneath the plane of the operating table and away fromknees and feet of operating surgeons and may be a few feet from the siteof recording electrode placement.

Recording electrodes are typically designed with adequate lead length tospan this distance. However, the longer length renders the electrodesmore susceptible to electromagnetic and mechanical artifacts. Deviceswith separate head boxes for stimulating and recording electrodes allowplacement of the recording portion closer to the site of electrodeplacement without affecting the accessibility of the stimulationportion. However, the separate arrangement is less popular, possibly dueto cost or to perceived complexity of setup with two separate cables andconnection housings.

The embodiment shown in FIG. 5 involves the incorporation of bothstimulation and recording electrodes with a single cable, but with thehead boxes for recording and stimulation arranged in a staggered fashionalong that cable. The recording electrode portion appears at theterminal end of the cable and can be placed at the site of recordingelectrode placement. This arrangement allows use of shorter lengthelectrodes, which may be cheaper to construct and less susceptible toelectromagnetic and mechanical (drape movement) artifacts. The stimulusportion is positioned more proximate to the main unit by several feet(for example, 6 feet). After the recording portion is properlypositioned, the stimulus connection box will be approximately at itsoptimal positioning for access after surgical draping. The all-in-oneconstruction would obviate the need to separately place a stimulus headbox apparatus, as for devices that include separate recording andstimulation head boxes and associated cabling.

In particular, the FIG. 5 embodiment involves a modification of thedevice illustrated in FIGS. 3A-3G. While the apparatus shown in FIGS.3A-3G includes connections for only recording electrodes, the FIG. 5embodiment includes both stimulating and recording electrodeconnections. The main unit connector 510 includes connections to theelectrical stimulus source(s) in addition to connections for recordingand automatic setup. Similarly, from the main connector, the main cable520 contains wires to carry stimulus current, as well as, wires forrecording and automatic setup.

The stimulator “head box” 530 may be permanently fixed or detachablyattached to the main cable and has attached straps 540 (e.g., Velcro) inorder to support the box in an appropriate fashion to the undercarriageof the operating table. The head box 530 (or connection unit) providesstandard “protected” connection termini 550 to accommodate one or morepairs of stimulus probe (cathode) and anode electrodes. For example, theexemplary embodiment in FIG. 5 shows two separate pairs of stimulatorconnections S1 and S2.

A portion of the cable 560 continues beyond the bead box 530 toward itsterminus connector 570. This portion of the cable 560 carries only thewires associated with recording and automatic setup. The cable 560terminates in a connector 570, that accepts patient-connection kits asdescribed above, or an adapter, which accepts standard protected pinconnectors.

While this invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart. Accordingly, preferred embodiments of the invention as set forthherein are intended to be illustrative, not limiting. Various changesmay be made without departing from the spirit and scope of theinvention.

For example, the connector type described above is exemplary andtherefore not critical to the above embodiments. In addition, thepossible conditions of the extra pairs of electrode leads carryinginformation regarding setup instructions, need not be limited to anyparticular circuitry. For example, a straight jumper connection may bereplaced by fixed resistors of varying value. The values may be chosenso that they are sufficiently different from one another to allow aprobe circuit from the main unit to easily differentiate whichresistance values are present. The pattern of open circuit andresistance among the extra electrode pairs will give a much greatervariety of potential information that might be transferred to the mainunit. Furthermore, the stimulus electrodes may be also be connected tothe cable 560 in any fashion either fixed or attachable.

What is claimed is:
 1. A connection system for a nerve integritymonitoring system, the nerve integrity monitoring system having meansfor receiving and/or transmitting recording, set-up and stimulussignals, the connection system comprising: one or more firsttransmission lines having a first connector at a first end and a secondconnector at a second end, at least one said connector adapted to beconnected to the receiving and/or transmitting means, the one or morefirst transmission lines carrying at least said recording, set-up andstimulus signals to and from the receiving and/or transmitting means;and a connection unit attached to the one or more first transmissionlines between the first and second connectors, wherein one or moresecond transmission lines carrying the stimulus signals are connected tothe connection unit.
 2. The apparatus of claim 1, wherein the firstconnector is adapted to be coupled to the nerve integrity monitoringsystem, and allows transmission of recording, set-up and stimulussignals to and from the nerve integrity monitoring sdystem.
 3. Theapparatus of claim 1, further comprising at least one of recordingelectrodes, set-up electrodes, combined recording/set-up electrodes, arecording harness, a set-up harness, a recording and set-up harness, andan adapter that is adapted to be attached to a patient, wherein thesecond connector is coupled to at least one of said recordingelectrodes, set-up electrodes, combined recording/set-up electrodes, arecording harness, a set-up harness, a recording and set-up harness, andan adapter that is adapted to be attached to a patient, the secondconnector allowing transmission of recording and set-up signals.
 4. Theapparatus of claim 3, wherein the connection unit operates to divide theone or more first transmission lines into a first segment and a secondsegment, the first segment having the first connector and allowingtransmission of recording, set-up and stimulus signals, and the secondsegment having the second connector and allowing transmission ofrecording and set-up signals to and from at least one of the recordingelectrodes, set-up electrodes, combined recording/set-up electrodes, arecording harness, a set-up harness, a recording and set-up harness, andan adapter that is adapted to be attached to a patient.
 5. The apparatusof claim 1, further comprising stimulus probe and anode electrodes andwherein the one or more second transmission lines are attached to thestimulus probe and anode electrodes.
 6. The apparatus of claim 1,wherein the connection unit includes an attachment device thatpermanently fixes the connection unit to the one or more firsttransmission lines.
 7. The apparatus of claim 1, wherein the connectionunit includes an attachment device that allows the connection unit to bedetachably attached to the one or more first transmission lines.
 8. Theapparatus of claim 1, wherein the connection unit includes an attachmentdevice that allows the connection unit to be detachably attached to anoperating table.
 9. A nerve integrity monitoring system, comprising: theapparatus of claim
 1. 10. A nerve integrity monitoring systemcomprising: means for receiving and/or transmitting recording, set-upand stimulus signals; one or more first transmission lines having afirst connector at a first end and a second connector at a second end;one or more second transmission lines having one or more connectors; aconnection unit positioned between the first and second connectorscomprising: a first attachment means for attaching the one or more firsttransmission lines to the receiving and/or transmitting means; the firstconnector for connection to the receiving and/or transmitting means andallowing transmission of recording, set-up and stimulus signals to andfrom the receiving and/or transmitting means; and a second attachmentmeans for receiving said one or more connectors from the one or moresecond transmission lines, wherein the one or more first transmissionlines carry at least said recording, set-up and stimulus signals to andfrom the receiving and/or transmitting means and the one or more secondtransmission lines carry said stimulus signals.
 11. The nerve integritymonitoring system of claim 10, wherein the first attachment devicepermanently fixes the connection unit to the one or more firsttransmission lines.
 12. The nerve integrity monitoring system of claim10, wherein the first attachment device allows the connection unit to bedetachably attached to the one or more first transmission lines.
 13. Thenerve integrity monitoring system of claim 10 further comprisingstimulus probe and anode electrodes adapted to be received by the secondattachment means, wherein the one or more second transmission lines areattached to the stimulus probe and anode electrodes.
 14. The nerveintegrity monitoring system of claim 10, wherein the first attachmentmeans allows the connection unit to be detachably attached to anoperating table.
 15. The nerve integrity monitoring system of claim 10,wherein the second attachment means includes at least one of maleconnectors and female connectors.
 16. A method for operating a nerveintegrity monitoring system, comprising: transmitting at leastrecording, set-up and stimulus signals to and from the nerve integritymonitoring system using one or more first transmission lines having afirst connector at a first end and a second connector at a second end;and transmitting stimulus signals using one or more second transmissionlines connected to a connection unit, the connection unit being attachedto the one or more first transmission lines between the first and thesecond connectors.